(a) Field of the Invention
This invention generally relates to power wrenches for turning threaded connection members on flanges and the like.
(B) Description of the Prior Art
Power wrenches for turning threaded connection members, such as nuts and bolts, are described in U.S. Pats. 2,972,918 and 3,706,244 which are only typical of such patents. U.S. Pat. No. 3,706,244 describes a power wrench having a reaction-support structure with a limited range of adjustability for different patterns of the connection members.
In power wrenches of the foregoing type it is desired to maintain a substantially perpendicular relationship between the piston rod of the power cylinder and the wrench, at mid-stroke of the rod. The desired perpendicularity is based on the fact that by limiting the rotation of the wrench arm to a relatively small angle in response to a full stroke of the piston rod, and by making this right angle relationship to become established at the rod's mid-stroke, the torque produced by the power cylinder can be fairly accurately measured by measuring only the pressure applied to the piston in the power cylinder.
In view of the limited range of adjustability afforded by the known reaction support structures for the power cylinder, there was a requirement to use different reaction-support structures for distinctly different patterns of connection members. The need to stock such different reaction-support structures and to change them in the field was very time consuming and therefore expensive.
When a power wrench is designed for a specific pattern of connection members, the reaction-support structure is such that the desired right-angle relationship between the piston rod and the wrench can be maintained for any position of the reaction structure when supported from any pair of connection members within said specific pattern. In this manner maximum torque will be obtained per unit of pressure applied to the power cylinder, and torque measurements can be sufficiently accurately made by simply measuring the pressure applied to the power cylinder.
There was a long-felt need for a power wrench having an easily-adjustable reaction-support structure over a wide range of connection member patterns, and being capable of maintaining the right-angle relationship between the piston rod and the wrench over the entire range of adjustability for the reaction support.